Pressure relief covers for frozen food containers

ABSTRACT

Undesired bulging of sealed food containers occurring during blast freezing is overcome by providing covers with pressure-relief passageways or vents in the form of a plurality of depressions in the region where the covers contact the upper edge of the containers to which they are applied. An alternative, but less preferable, embodiment is to form shallow slots in the upper edges of the containers.

This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/701,227, filed Jul. 21, 2005 by David W. Diamond for “Pressure Relief Covers For Frozen Food Containers.”

FIELD OF THE INVENTION

This invention relates to the art of blast freezing foods in sealed containers and more particularly to covers for such containers.

BACKGROUND OF THE INVENTION

A variety of foods are frozen in plastic containers of one gallon capacity or more for institutional customers, e.g., restaurants, hospital and military commissaries, and other food manufacturers. Examples of such foods are eggs, ice cream, puddings, mashed potatoes, dairy products, and stewed and cooked fruits. The blast freezing process involves putting a food product into plastic containers having a generally flat bottom wall, applying a snap-fit plastic cover to the container, and then placing the covered container into a blast freezer where it is subjected to blast freezing. In a typical commercial blast freezing operation a number of such covered containers are arranged in vertical stacks on a pallet (or other device of like purpose) and the stacks of containers are transported into the blast freezer via the pallet. In some cases the cover may include a gasket to assure a tight seal with the container. However, it is common to use a cover without a gasket, in which case the cover makes direct contact with the top edge of the container.

A typical industry practice is to fill the container about 1.5 inches from the top before being capped with a cover and then subjected to blast freezing. The 1.5 inches spacing is designed to accommodate the fact that some creamy foods tend to cone during filling, so that the food is higher at the center than at the side wall of the container. Notwithstanding that spacing, it has been observed that in certain cases when such foods are converted to a frozen mass by blast freezing, a pressure increase in the container presses the frozen mass down away from the container cover, forcing the bottom of the container to bulge outwardly (i.e., downwardly) into a domed shape. No clear explanation has been agreed upon for this phenomenon. However, the problem is objectionable because the stacked containers are not usually strapped down, and consequently the top container tends to fall off readily due to its bulging bottom. The problem appears to be confined to the top containers in each stack, possibly because the lower containers in each stack are carrying the weight of the higher containers when they are frozen.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention solves this problem by providing covers with a plurality of depressions in the region where the covers contact the upper edge of the containers to which they are applied. An alternative (but less preferable) embodiment is to form shallow slots in the upper edges of the containers.

FIG. 1 is a side elevation of a container which is described hereinafter in connection with a cover embodying the invention.

FIG. 2 is a longitudinal sectional view of the same container taken along line 2-2 of FIG. 1.

FIG. 3 is bottom view of the same container.

FIG. 4 is an enlarged view of a detail of the container.

FIG. 5 is a plan view of a cover for the container.

FIG. 6 is a side elevational view of the same cover.

FIG. 7 is a bottom view of the cover.

FIG. 8 is a cross-sectional view of the cover.

FIG. 9 is a sectional view taken along line 9-9 of FIG. 7.

FIG. 10 is a sectional view like Fig, 9 but taken along line 10-10 of FIG. 5 through the tear tab.

FIG. 11 is a plan view of a like container modified according to a second embodiment of the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

FIGS. 1-10 illustrate a conventional plastic container 2 and cover 4 designed for the frozen food industry, except that the cover has been modified to constitute a preferred embodiment of the invention. The container and cover are made of a suitable resilient plastic, e.g. polyethylene. The container comprises a bottom wall 6 and a tapered side wall 8. The side wall 8 has an outwardly projecting peripheral locking flange or bead 10 at its upper end, an outwardly projecting peripheral seating flange 12 spaced below locking flange 10, and an outwardly projecting peripheral flange 14 that forms a support for a skirt or secondary side wall 16 that surrounds and is spaced from side wall 8. The upper end surface of locking flange 10 is an extension of and forms part of the upper end surface 11 of the container. Portions 16A of skirt 16 are spaced far enough from side wall 8 to permit a person's fingers to grip its bottom edge with enough purchase to be able to lift and carry the container with its contents. By way of example but not limitation, the container may have four equally circumferentially spaced portions 16A as shown in FIG. 11.

The cover 4 comprises a central crown or body portion 20 and a rim portion 22. Preferably but not necessarily, the center of body portion 20 has an annular raised section 24 for both aesthetic and strength reasons. The rim portion 22 comprises an annular inclined inner wall 26 that projects upwardly from crown portion 20, a top circular flange 28 attached to the upper end of inner wall 26, an intermediate wall 30 attached to and depending from flange 28, and an outer wall 32 attached to and surrounding flange 28. Preferably, but not necessarily, outer wall 32 is slanted downwardly and outwardly. An annular channel 34 (FIG. 10) is formed between intermediate wall 30 and outer wall 32 and is sized to accommodate the upper end of container 2, as explained hereinafter. The curved annular undersurface 35 that defines the upper end of channel 34 is uniform along its full circumference, except as modified by the present invention as hereinafter described. The bottom edge 36 of outer wall 32 projects below crown portion 20, while preferably, but not necessarily, the bottom edge 38 of intermediate wall 30 terminates short of the bottom surface of the crown portion.

The outer wall 32 is designed to make a locking connection with locking flange 10 of container 2. For this purpose a plurality of circumferentially-spaced locking ribs 40 (sometimes referred to as “undercuts” in the molding art) are formed on the inner surface of outer wall 32, with the ribs extending into the channel 34. The cover illustrated in the drawings has eight ribs 40 (FIG. 7). Each rib is tapered inwardly toward intermediate wall 30, having a triangular configuration in cross-section with its flat upper surface 42 serving as a shoulder that can make a locking connection with the underside of locking flange 10 of the container and its inclined bottom surface 44 serving to provide a cam action that forces wall 32 to bend outwardly to allow the rib to pass by locking flange 10 when the cover is forced onto the container. Attachment of the cover to the container results in the top end surface 11 of the container being engaged by the undersurface 35 of flange 28 of the cover, so that the under surface 35 will be tightly seated against that top end surface 11 when the foregoing container filled with a food product and with the cover in place is subjected to blast freezing.

Outer wall 32 also is designed so that part of it functions as a tear-away skirt. To that end the inner surface of wall 32 is formed with a score line 46 that extends for substantially the full circumference of the cover and intersects a rectangular opening 48 (FIGS. 6 and 10) in wall 32. Score line 46 subdivides outer wall 32 into a top container-locking section 50 and a bottom skirt section 52 (FIGS. 9 and 10). The bottom side of opening 48 is defined by two narrow wall sections 54 and 56 that together form a tear tab. Wall section 54 is undercut on its inner side surface to facilitate rupturing its connection to wall 32. Wall section 56 is formed with a plurality of narrow vertical ridges 60 on its exterior surface to facilitate gripping. When wall section 54 is ruptured, the resulting tab comprising wall sections 54, 56 can be gripped to tear away the skirt section 52 along score line 46. The outer wall 32 is sized so that when the cover is applied to the container so that locking ribs 40 are interlocked with locking bead 10, the bottom edge of outer wall 32 will lie immediately adjacent to or engage seating flange 12, making it difficult for a person to grip the bottom edge of outer wall 32 with enough purchase to effect removal of the cover. However, if the skirt section 52 is torn away, the resulting gap between the bottom edge of locking section 50 and seating flange 12 will be sufficient to permit a person to grip that bottom edge to pry the cover off of the container.

To the extent just described, the foregoing construction is well known.

For the present invention that construction is modified by providing depressions 64 (FIGS. 7 and 9) in the bottom surface 35 of top flange 28. Preferably the depressions 64 are formed in the regions between the locking ribs 40, as shown in FIG. 7. Alternatively depressions 64 could be formed in vertical alignment with locking ribs 40, but having them between the ribs is preferred since it is believed to provide faster, better pressure relief. The depressions may be relatively shallow. Preferably they are formed with a depth in the range of about 0.015 inch to about 0.025 inch, e.g., about 0.020 inch. The length of depressions 64, i.e., their dimension in a circumferential direction, can vary. In the illustrated preferred embodiment, the depressions extend for the full length of the gap between adjacent locking ribs 40 which may, for example, be about 1 inch for a cover having a maximum outside diameter of about 11.5 inches. The width of depressions 64, i.e., their radial dimension, also is variable, but should be great enough to allow them to provide small gaps between the upper end surface 11 of the container and the bottom surface 35 of top flange 28 that can function as pressure relief passageways or vents for the container, with the pressure relief being sufficient to prevent the bulging out of the bottom walls of any of the containers after blast freezing. By way of example but not limitation, the depressions 64 may have a width in the range of about 0.024 inch to about 0.60 inch in the case of a lid having a maximum outside diameter of about 11.5 inches.

FIG. 11 pertains to an alternative embodiment of the invention which consists of using a conventional cover as described above (i.e., a cover without the depressions 64), and modifying the container 2 by forming shallow slots 70 in its upper end surface, which in this case is the upper end surface 11 of the container. In the illustrated embodiment four slots 60 are provided, each in line with one of the expanded portions 16A of skirt 16, but it is to be understood that they may be located at other points around the container and also that the number of slots may be varied, as indeed is true of the number of depressions 64 in the cover of the preferred embodiment of the invention. It is to be noted also that slots 70, and also depressions 64, need not be spaced symmetrically as shown. The depth of the slots is in the range of about 0.015 inch to about 0.025 inch, preferably about 0.020 inch. By way of example but not limitation, their length measured along the circumference of the container may be varied and, for example, may be in the range of about 0.50 inch to about 1.00 inch.

The radial dimension of slots 70, i.e., their width, is great enough to enable them to provide gaps between the top end 11 of the container and the undersurface 35 of flange 28 when the cover is locked in place. In the illustrated embodiment the top end surface 11 of locking flange 10, is radiused, sloping downwardly and outwardly away from the center axis of the container (see FIG. 4), with the consequence that in FIG. 11 the slots 70 appear to stop short of the outer margin of locking flange 10. However, due to the sloping nature of end surface 11, slots 70 still can function as passageways for venting the container. It should be understood also that the container's upper end surface 11 (which includes the upper end surface of locking flange 10) could extend in a horizontal plane, i.e., at a right angle to the longitudinal axis of the container, in which case the depressions would extend for the full width of upper end surface 11, i.e., from the inside surface of the container to the outer boundary of locking flange 10.

Further with reference to FIG. 11, when a cover is applied to the container so that the under surface 35 of top flange 28 (without the depressions 64) engages the upper surface 11 of the container, the slots 70 will serve as pressure release passageways, yielding substantially the same protection as the preferred embodiment of the invention against deformation of the bottom wall of the container as a consequence of blast freezing of its contents.

The invention is susceptible to a number of modifications. Thus the dimensions, the number and the spacing of depressions 64 and slots 70 are selected to achieve the optimum pressure relief effect. Although the invention is described in connection with a cover having a tear skirt, it also is applicable to other forms of so-called snap-fit covers that have locking ribs (“undercuts”) that releasably interlock with a locking flange or like member on the container to provide a secure connection, including but not limited to covers that are adapted for stacking filled containers one upon the other. Similarly, the invention may be practiced with other forms of containers. For example, the locking flange or bead 10 may be located below the upper end of the container, in which case the slots 70 of the alternative embodiment of the invention described in relation to FIG. 11 would be formed in the upper end edge of the container but not in the upper end surface of the locking flange. Another possible modification is to utilize a combination of one or more depressions in the cover and one or more slots in the upper end edge of the container. Still other modifications and embodiments of the invention will be obvious to persons skilled in the art. 

1. A container and lid combination for use in freezing and storing fruit or other food comprising: a plastic container comprising a side wall and a bottom wall formed integral with said side wall, said side wall having a top edge and an outwardly protruding locking flange; and a plastic cover comprising a body portion and a rim formed integral with and surrounding said body portion, said rim comprising an annular flange surrounding said body portion and an annular wall attached to and depending from said annular flange in spaced relation to said body portion, said annular wall having means for interconnecting with said locking flange so as to secure said cover to said container in covering relation to the interior space of said container with said annular flange overlying and engaged with said top edge of said container; characterized by pressure-relief passageways between said cover and said container in the region where said annular flange of said cover is engaged with said top edge of said container.
 2. A container and lid combination according to claim 1 wherein said passageways are formed by mutually spaced depressions in said annular flange.
 3. A container and lid combination according to claim 2 wherein said annular flange has a bottom surface, and said depressions are formed in said bottom surface.
 4. A container and lid combination according to claim 1 wherein said depressions have a depth in the range of about 0.015 inch to about 0.025 inch.
 5. A container and lid combination according to claim 1 wherein said passageways are formed by mutually spaced slots in said top edge of said container.
 6. A container and lid combination according to claim 4 wherein said slots have a depth of about 0.015 inch to about 0.025 inch.
 7. A container and lid combination for use in freezing and storing fruit or other food comprising: a plastic container comprising a side wall and a bottom wall formed integral with said side wall, said side wall having a top edge with an outwardly protruding bead; and a plastic lid comprising a body portion and a rim formed integral with and surrounding said body portion, said rim comprising an inner wall section extending at an angle to said body portion, an outer wall section concentric with said inner wall section and forming a skirt, and an intermediate wall section disposed between said inner and outer wall sections, with said body portion having a top surface and a bottom surface and said intermediate wall section projecting above said top surface and said outer wall section extending below said bottom surface, said outer wall section having means for interconnecting with said bead so as to secure said lid to said container in covering relation to the interior space of said container with said intermediate wall section overlying and engaged with said top edge of said container; characterized by pressure-relief passageways between said lid and said container in the region where said lid is engaged with said top edge of said containers.
 8. A container and lid combination according to claim 7 wherein said passageways are formed by mutually spaced depressions in said intermediate wall section of said rim.
 9. A container and lid combination according to claim 8 wherein said intermediate wall section has an underside, and said depressions are formed in said underside.
 10. A container and lid combination according to claim 8 wherein said depressions have a depth in the range of from about 0.015 inch to about 0.025 inch.
 11. A container and lid combination according to claim 7 wherein said pressure-relief passageways are in the form of shallow slots in said top edge of said container.
 12. A container and lid combination according to claim 11 wherein said slots have a depth in the range of from about 0.015 inch to about 0.025 inch.
 13. A container and lid combination according to claim 7 wherein said bead has a top surface that is an extension of said top edge.
 14. A container and lid combination according to claim 13 wherein said top surface is slanted downwardly and outwardly from said top edge.
 15. A plastic cover for making a snap fit with a container that has a top edge and a locking flange extending around its container's periphery at or adjacent to its top end edge for interlocking with said cover, said plastic cover comprising a crown and a rim formed integral with and surrounding said crown, said rim comprising an inner wall section, an outer wall section concentric with said inner wall section and forming a skirt, and an intermediate wall section disposed between and connecting the upper ends of said inner and outer wall sections, with said crown being recessed below said intermediate wall section and said outer wall section extending below said crown, means on the inside of said outer wall section for interlocking with a locking flange on the periphery of a container so as to lock said cover to the container, and a plurality of depressions formed in said inner wall section for providing pressure-relief passageways between said cover and a container to which said cover is attached.
 16. A plastic cover according to claim 15 wherein said cover has a plurality of internal locking projections for interlocking with a locking flange on a container, and further wherein said depressions are located between adjacent ones of said locking projection. 